The present invention relates generally to dome type building structures, and more particularly to an improved dome structure and method of making same which enable on-site construction of dome buildings of substantially greater size than heretofore obtainable.
Dome type building structures made by inflating an inflatable form and applying an insulating foam material interiorly of the inflated form followed by securing a reinforcing mesh to the foam layer and applying one or more layers of a cementitious material to the foam layer so as to embed the reinforcing mesh are generally known. See, for example, U.S. Pat. Nos. 3,277,219 and 4,155,967 that are incorporated herein by reference. In many applications, such structures provide significant economic advantages over conventional building constructions employing lumber, bricks, concrete blocks and the like and taking conventional rectangular or other generally square corner structural configurations. The economic advantages of buildings constructed with inflatable forms having insulation foam and concrete layers applied to their inner surfaces derive in part from the relatively short period required to construct such buildings as compared with conventional building techniques. In general, such dome type building structures are made by securing the periphery of the inflatable form to a footing or foundation, inflating the form, applying an insulating foam layer against the interior surface of the inflated form as by spraying, attaching a relatively rigid reinforcing grid or mesh to the interior surface of the cured foam layer, and thereafter applying one or more cementitious layers, again as by spraying, to the foam layer so as to embed the reinforcing mesh and provide a self-supporting shell-like dome structure.
Dome shaped building structures of the aforedescribed type have proven to be structurally sound and particularly environmentally compatible due to their relatively high thermal efficiency. One drawback to these known dome structures is that they are restricted in size. As the inflatable form is made larger to produce a larger diameter dome, such as a diameter exceeding 300-400 feet, the higher air pressure required to inflate and raise the heavier form may cause the form to tear. In addition, if the wall thickness of a large size dome shell is made sufficiently thick to theoretically provide the necessary strength for self-support, the weight of the additional concrete may exceed its increased strength so that inward buckling occurs, generally termed "snap through" or "oil can" buckling.
Attempts have been made to overcome the size limitations of dome-type buildings by employing a rigid skeletal framework of struts or tubular members to define the contour of the desired building. See, for example U.S. Pat. No. 4,442,059. The struts or tubular members are secured together at intersections by clamps with the lower struts fixed to a base or foundation. An air-impervious membrane envelope is provided within the framework and is inflated to place the struts or tubular members in tension. A coating, such as a fiber-reinforced resin or cement, is applied to the outside surface of the membrane to cover both the membrane and framework. After the desired coating thickness is allowed to set, the air pressure is released and the membrane removed whereupon the struts or tubular members return to a non-tensioned state and detach from the exterior coating material on the membrane. The inner surface of the construction may then be sprayed with resin to cover at least the strut connecting clamps.
U.S. Pat. No. 5,408,793 discloses a dome structure wherein a membrane is inflated to a desired dome shape against radial members made of steel wire, wire rope or glass or carbon fibers and having their bottom ends secured to a base on which the dome is built. The interior and exterior surfaces of the inflated membrane are coated with a rigidifying material such as shotcrete which hardens to form a structural composite layer with the membrane and radial wires embedded in the rigid composite layer. Circumferential high-tensile tensioning elements may be applied around the structure internally of the composite layer to counteract outwardly directed bursting forces created by materials contained within the finished dome.
While the dome structures of the type disclosed in U.S. Pat. Nos. 4,442,059 and 5,408,793 have enabled domes of larger size to be constructed, they have not altogether eliminated the problem of snap-through or oil can buckling when very large domes, such as domes having base diameters significantly greater than 300 feet, are constructed. Such domes have the further disadvantage that they are relatively complex and expensive to make, as compared to a dome structure as disclosed in U.S. Pat. No. 4,155,967. Thus, a dome structure of the type disclosed in the latter patent but which can be built to a relatively large size without significantly increasing the wall or shell thickness would provide a substantial advance in the dome building art.